The present invention relates to an accumulated semi-active hydraulic damper, more particularly one, in which an accumulator is exploited for relieving, and storing excessive pressure of the hydraulic oil of the circuit in the energy reducing operation thereof and which can achieve a relatively high damping ratio while it is not constructed of sophisticated control devices that are relatively expensive.
There are many conventional vibration counteracting methods for engineering constructions, which are:
1. Base isolation; in this method, a passive damping material such as elastic compound or other energy absorber is interposed between the structure and the foundation. The advantage of this method is that natural frequency of the structure will be reduced to avoid the primary frequency range of the earthquake, while the disadvantage is that the damping ratio would be greatly reduced if the structure is a long period one or situated near a fault zone.
2. Active control; in this method, online monitoring of the structural vibration response is exploited wherein data on relative displacement, velocity and acceleration of the structure subject to vibration is analyzed and calculated for determining the amount of force to be applied to counteract the vibration, and it requires an actuator of quick frequency response. Therefore, a lot of sophisticated devices such as vibration sensors, data acquisition devices, online computers, servo controllers, and precise actuators are needed, making the cost significantly increase. The need of continuous electric power supply to function makes active control have the disadvantage of low reliability in light of the fact that earthquake is often followed by power failure. Currently, active control has not been put to use for counteracting vibration of earthquake.
3. Passive control; a damping device of this type doesn""t have to be regulated in amount of force, and is not provided with function of monitoring the structural vibration response; a passive damper is ready to function immediately after it is installed. There are two main types of passive controls, which are dynamic interaction method and energy dissipation method. The dynamic interaction method applies a sub-oscillator, which is installed on the structure subject to vibration, and is relatively light in weight as compared with the structure, and has a self-oscillation frequency that is the same as, or approximates to, that of the structure, therefore the sub-oscillator can reduce the effect of vibration of the structure. This method is usually installed on uppermost portions of high buildings or long bridges to reduce the oscillation caused by wind. The disadvantage of dynamic interaction method is that accurate analysis on the mechanical property has to be done previously, otherwise the vibration reducing effect will decrease. An example of energy dissipation method is the use of steel plate with specific shape in a structure; the energy of motion of the structure caused by earthquake is dissipated by means of the hysteretic behavior that is caused when the steel board is experiencing plastic deformation. The cost of the energy dissipation method is relatively low. However, steel plate is subject to low cycle fatigue when the plastic deformation happens in a two-way manner repeatedly. And, it is not suitable for reducing the effect of wind. Another example of energy dissipation method is the use of a hydraulic damper, which has a sealed container having liquid therein; the viscous damping of fast flowing liquid in the container will exert negative work to the structure to reduce vibration. The hydraulic damper can reduce displacement and acceleration of the structure, and won""t have residual deformation. However, its self oscillation frequency is too low, and the viscous damping has very limited effect.
4. Semi-active control; Semi-active control method has the adaptability of active control method as well as the reliability and low power consumption of passive control method. Semi-active control methods are usually provided by means of improving passive control methods. According to experiments, a large damping coefficient of a damper doesn""t guarantee satisfactory energy damping performance, while a relatively small damping coefficient might help the damper work with suitable timing to have best performance. For instance, a semi-active damper with continuous control of force, patented by Taiwan Patent Office with no. 339396, has a sensor, and two precision flow rate control valves or proportional valves to sense the response of the structure, and to continuously control the amount of force of the damper respectively. These precision valves will cause a large increase of the cost of the damper. Because the primary purpose of such damper is to reduce the relative displacement of various portions of the structure, continuous control seems unnecessary.
From the above analysis, we have conclusions as followings:
1. Active control method provides the best performance.
However, it is very expensive to construct, and has problem of stability yet to be dealt with. Therefore, active control has not been put to use for counteracting vibration of earthquake.
2. Base isolation is not suitable for use with structures that are of long cycle type or situated near a fault zone.
3. The fact that passive control is not suitable for reducing the vibration caused by wind and various types of earthquakes gives rise to the development of semi-active control. However, there is not much difference between conventional dampers of semi-active control type and active dampers because semi-active control still emphasizes continuous control and optimization, resulting in the use of sophisticated servo controllers and precision flow rate control valves that make semi-active dampers nearly as expensive as active ones.
It is a main object of the present invention to provide an accumulated semi-active hydraulic damper, which can provide a relatively good damping effect, and is easy and inexpensive to construct.
The damper of the present invention includes a cylinder, an accumulator, an oil box, and directional control components. The cylinder body is connected to a lower joint of a structure at one end, while the piston rod is connected to an upper joint of the structure, or reverse.
The directional control components include a directional control valve, a first primary oil circuit, and a second primary oil circuit. The directional control valve can switch among various positions thereof according to a signal of the sensor, which is translated from movement of the structure sensed by means of the sensor. The directional control valve is connected to both the oil box and the accumulator. The first oil circuit is connected to the first port of the cylinder body, and connected to the directional control valve. The second oil circuit is connected to the second port of the cylinder body, and connected to the directional control valve.
Thus, vibratory movement of the structure that causes a displacement of the upper joint relative to the lower joint can be counteracted when the sensor senses the movement to make the directional control valve switch among positions thereof such that hydraulic oil of the accumulator can flow through suitable one of the ports of the cylinder body to move the piston rod in a direction opposite to the displacement.